The present invention relates to a bis(1,1,3,3-tetramethylbutyl)phosphinic acid compound. The present invention also relates to a method of extracting and separating cobalt and/or nickel which is contained in an aged electroless nickel plating solution. In particular, it relates to a method of selectively separating cobalt and/or nickel which is contained in an aged electroless nickel plating solution in a large amount, with a bis(1,1,3,3-tetramethylbutyl) phosphinic acid compound.
Currently, electroless plating technique finds extensive application in various fields such as production of ornamental plated articles and production of functional electronic components including magnetic discs and magnetic tapes. Regarding the metals to be plated, in addition to the nickel which has been heavily used so far, nickel-cobalt alloy has also been used in part.
Electroless plating is generally carried out by immersing a base material to be plated in a plating solution of an initially made-up plating bath, to undergo reaction for an empirically determined length of time. However, even though the plating bath and process conditions are properly controlled for the treatment, the increase of the oxidation product during the reaction is unavoidable, and the treatment solution which has been used to some extent becomes not re-usable any more. Accordingly, the solution which has been subjected to a predetermined level of plating reaction is often discarded as an aged plating solution, even though a large amount of a plating metal ion such as Ni.sup.2+, accompanying Co which cannot be separated from Ni, and a reducing component such as sodium hypophosphite still remain in the solution.
It has been difficult so far to separate nickel from cobalt. As one such separating method, a solvent extraction process utilizing a dialkyl phosphinic acid compound derived from a dialkyl phosphine has been known (Japanese Patent Laid-Open Sho 57-73412, Japanese Patent Laid-Open 57-73143, Japanese Patent Laid-Open 61-44139, Japanese Patent Laid-Open 1-315384, and Japanese Patent Laid-Open 6-264156.)
However, a bis(1,1,3,3-tetramethylbutyl)phosphinic acid compound of the present invention is not disclosed in the above-mentioned publications, and a method of separating cobalt and nickel contained in an aged electroless nickel plating solution has not yet been known.
As a phosphinic acid compound, bis(2,4,4-trimethylpentyl) phosphinic acid which is represented by the following formula (5) and a production method thereof are disclosed (U.S. Pat. No. 4,374,780). ##STR2##
According to the method of producing the dialkylphosphinic acid specified in that patent, phosphine and diisobutylene (a mixture of 2,4,4-trimethylpentene-1 in an amount of 70%, and 2,4,4-trimethylpentene-2 in an amount of 30%) are reacted by using a free-radical catalyst to produce a dialkyl phosphine, then said product is reacted with an oxydizing agent to produce a dialkylphosphinic acid.
However, radical addition reaction in the reaction between said phosphine and diisobutylene has no reaction selectivity, and generally a mixture of mono, di-, and tri-alkylphosphines is produced. Accordingly, it is difficult to increase the generation ratio of the dialkylphosphine selectively. Thus, the yield of the dialkylphosphinic acid which is derived from the dialkyl phosphine according to above-mentioned reaction has been low.
In view of above-mentioned facts, the present inventors as a result of carring out an intensive study to find a phosphinic acid compound which is useful as an extracting agent for metals such as cobalt, and discovered that a bis(1,1,3,3-tetramethylbutyl) phosphinic acid, which is a new dialkylphosphinic acid compound, a production method thereof and its usefulness thereof as an extracting agent for metals to complete the present invention.
Further, the present inventors found that said new bis-(1,1,3,3-tetramethylbutyl)phosphinic acid compound is useful as an extracting agent for cobalt and/or nickel contained in an aged electroless nickel plating solution and completed the present invention.